While wood is widely utilized as building materials, crafted products and the like, it is a common practice that wood is coated or impregnated with various treating agents such as high-molecular weight compounds, low-molecular weight compounds, chemical agents and inorganic materials for the purpose of improving wood properties such as dimensional stability, and resistances to water, staining, fire, rotting, crazing and wear.
Among these agents, many attempts have been made to apply to wood the silicones which have been proven effective as modifiers for paints and resins with respect to water repellence and stain resistance. For example, JP-A 56-4408 discloses a method of coating a surface of wood with a composition comprising 100 pbw of a silicone diol having a relatively high viscosity and 0.1 to 50 pbw of a crosslinker, followed by curing. This method, however, detracts from the wooden quality on the wood surface, and has the drawback common to paints that the effect of protecting the wood interior disappears if the surface coating receives only a few flaws in the course of actual use of wood in various applications. When the above treatment is performed on the wood which has been internally impregnated with inorganic salts of phosphoric or boric acid serving as flame retardants or termite-controlling agents, undesirably the coating permits the inorganic salts to be readily leached out in rain water or the like.
Intending to apply the sol-gel method using silicon alkoxide to wood, JP-A 63-265601 discloses a method of preparing a modified wood by forming a silicone polymer within cell walls of wood. This method capable of forming a silicone polymer within wood has advantages that the wooden quality on the surface is not compromised and the effect lasts even after the wood surface flaws. However, catalysts such as hydrochloric acid or organometallic compounds must be used to promote curing because of the low reactivity of monomers, leaving the problems that preparation requires cumbersome operation and costs and the wood itself can be degraded by the catalyst.
Additionally, the silicone polymer forms via catalytic reaction while filling wood cell cavities therewith. Then it is effective for prohibiting water absorption to some extent, but less effective for improving dimensional stability.
Beside the silicone, SBR latex is coated to wood surface as the anti-crazing agent as disclosed in JP-A 54-110234. Due to poor stability over time, the latex coating degrades upon outdoor exposure, failing to prevent the chemical agents from being leached out.
As the anti-crazing paint for wood, JP-A 60-255866 describes a coating composition comprising an SBR or NBR latex and a polyalkylene oxide group-containing compound, which is coated to wood surface. The polyalkylene oxide group-containing compound is hydrophilic so that it is leached out upon exposure to weather over time, and the effect does not last.
JP-A 55-118044 discloses a wood treating composition having a low-volatile oligomer emulsified in water. JP-A 5-69412 discloses a wood treating composition comprising a water-soluble modifier and an emulsion. Both the low-volatile oligomer and the water-soluble modifier are hydrophilic compounds which can be leached out with the lapse of time, failing to maintain the desired effect. JP-A 4-307204 discloses a wood processing composition comprising a water-soluble filling/curing agent which cures after having penetrated into wood so that it prevents chemical agents from being leached out and restrains the wood from shrinkage. The water-soluble filling/curing agent comprising volatile reagents such as urea and formalin requires careful management of the working environment, and the effect of preventing leaching-out is insufficient due to water solubility.
Another approach is to substitute a water-soluble solvent such as polyethylene glycol for the bound water in cell membranes. However, the solvent once substituted will be leached out over time due to its water solubility.
The above-discussed technology relates to surface treating agents for treating wood having rot-proof and termite controlling agents already impregnated therein. Then at least two steps are involved, and so the overall process is cumbersome and uneconomical.